ccd astrometric measurements and historical data summary ... · anushree chaudhuri is a student...

Vol. 14 No. 1 January 1, 2018 90 Journal of Double Star Observations

Introduction More than forty percent of the stars in the observa-

ble universe are gravitationally bound to one or more stellar components. By observing binary and multiple star systems, astronomers can determine whether a pair is gravitationally bound, and, if they are, determine their elliptical orbit, and consequently, the masses of the system’s components. Since the mass of a star de-termines other properties, such as magnitude, spectral class, and luminosity, the accurate measurement of mass through binary star research is crucial to gaining a better understanding of the universe (Genet et al 2015). For this research, the candidate selection criteria were: presently visible with a Right Ascension (RA) between 10 and 16 hours to ensure the star was high enough in the sky to prevent atmospheric interferences, a separa-tion between five and fifteen arcseconds to prevent merging cells on the CCD image while still observing a relatively close system, a magnitude difference less than five to prevent merging of centroids in the star im-age, and a number of observations greater than two but less than ten because this study focused on systems which did not already possess orbital solutions. Sys-tems were chosen based on their proximity to these specifications.

Methods An observing list was created from the Washington

Double Star catalog (WDS), which contained systems matching the outlined specifications of separation, posi-tion angle, right ascension, differences in magnitudes,

and number of observations (Mason & Hartkopf 2015). After requesting and examining historical data for sev-eral final candidates, WDS 12182-4251 (DAM 1244) was chosen as it most closely aligned with the decided specifications. Historical data of DAM 1244 from the WDS was analyzed to confirm the decision.

CCD images of DAM 1244 were requested from

CCD Astrometric Measurements and Historical Data Summary of WDS 12182-4251

Anushree Chaudhuri1 and Grady Boyce

2

1. Westview High School in San Diego, CA 2. Boyce Research Initiatives and Education Foundation (BRIEF)

Abstract: Precise astrometric coordinates, separation, and position angle of proposed binary system WDS 12182-4251 (DAM 1244) were determined from CCD (charge-coupled device) imaging analysis. The measurements acquired largely align with previously collected data avail-able through databases such as the Washington Double Star (WDS) Catalog. Additionally, the historical data and other information available on this system have been gathered and examined.

Figure 1. Exterior view of iTelescope 32, located at the Sid-ing Spring Observatory in Australia.

Vol. 14 No. 1 January 1, 2018 Page 191 Journal of Double Star Observations


Telescope 32 (T32) in the iTelescope network, located at an elevation of 1122 meters at the Siding Spring Ob-servatory in Australia. T32, Figure 1, has a large CCD chip with a wide field of view, and a pixel scale of 0.63 arcseconds/pixel, complementing the imaging needs of this study.

Eight images were requested with varying exposure times and through different filters, as shown in Table 1.

The luminance filter was used to provide a broad-spectrum view of DAM 1244. The other filters were used to limit photons to specific regions of the electro-magnetic spectrum to narrow the stellar centroids for precise measurements.

Each individual image was processed through Max-im DL and plate-solved to embed the World Coordinate System (WCS) by comparing stars in the image against the UCAC4 catalog (Mason & Hartkopf 2012). MiraPro x64, a software from Mirametrics, was used to determine position angle (Theta), separation (Rho), and precise astrometric coordinates. The software located the centroids of the A and B components to accurately measure Theta and Rho between the stars. The meas-urements were recorded in a Microsoft Excel spread-sheet enabling statistical analysis of the data to deter-mine the mean, standard deviation, and standard error of the mean. Figure 2 is a sample CCD image before processing. Figure 3 displays a CCD image after plate-solving and making astrometric measurements with MiraProx64.

Results Table 2 shows the mean, standard error of the

mean, and standard deviation for DAM 1244 Theta and Rho. Precise astrometric coordinates as measured in this study are also provided. Table 3 shows the raw data from all the images taken in this study.

Figure 3. Processed CCD image of WDS 12182-4251 under a blue filter with an exposure of 120 seconds.

Figure 2. Unprocessed CCD image of WDS 12182-4251 under a blue filter with an exposure of 120 seconds.

Images Statistics Theta Rho Right Ascension Declination

8 Mean 179.20° 8.47" 12n 18m 09.79s -42° 50’ 34.11"

8 Standard Deviation 0.01° 0.04" 0.01 0.05

8 Standard Error of

the Mean 0.006° 0.019" 0.003 0.024

Table 2. The mean, standard error of the mean, and standard deviation for astrometric measurements of WDS 12182-425.

Filter Images Exposure

(seconds)

Luminance 2 60

Luminance 2 90

Hydrogen alpha 2 180

Red 1 120

Blue 1 120

TOTAL: 8

Table 1. Number of images with filter and exposure time.



Discussion

CCD Image Measurements No images were omitted from the final data as none

contained concerning errors in diffraction or saturation, despite the relatively small separation between the A and B components. However, it was noted that the im-ages under H-alpha filters experienced a substantial amount of image noise, Figure 4. Image noise is de-fined as random variations of brightness or color infor-mation and is usually produced by an excess of electri-cal fluctuation in the sensor/circuitry of a digital cam-era. The H-alpha images were taken with an exposure of 180 seconds; increasing exposure time for narrow spectrum filters, such as H-alpha, may help to improve image quality in the future. Plate-solving for all images was satisfactory.

WDS Historical Data Table 4 shows previous historical measurements

and data available for DAM 1244 from the US Naval

Observatory. Using Richard Harshaw’s (2014) classifi-cation system for common proper motion pairs (CPMs), the proper motion measurements for this system have been analyzed. Harshaw’s ratings are calculated by nor-malizing values using an addition of the proper motion vectors. This results in a calculated statistic, or “rating”, which classifies the pair’s motion. Ratings close to 0.0% indicate an orbital relationship, while ratings close to 100.0% indicate an optical pair. The A compo-nent of DAM 1244 has a proper motion of [-17 -19], while the B component’s proper motion is [-17 -25]. The system has a calculated rating of 0.002%, which indicates that it is a common proper-motion pair. Figure 5 shows a Microsoft Excel scatterplot of the XY coordi-nates of historical measurements.

SIMBAD Data A note included in SIMBAD, an online astronomi-

cal database, states that the A component of WDS 12182-4251 is at a distance of 844.3 kiloparsecs. As there are no references available for this statement, it is unclear if this data is accurate.

Epoch (Julian Date) Image Exposure

(seconds) Theta (°) Rho (")

2457845.39454 Luminance 60 179.245 8.4974

2457845.39454 Luminance 60 179.192 8.5004

2457845.39454 Luminance 90 179.215 8.4527

2457845.39454 Luminance 90 179.183 8.4878

2457845.39454 H-alpha 180 179.223 8.4711

2457845.39454 H-alpha 180 179.212 8.4767

2457845.39454 Red 120 179.214 8.4642

2457845.39454 Blue 120 179.190 8.4414

Table 3. Summary of raw data from CCD image measurements made in this study

Figure 4. An H-alpha image which experienced a significant amount of image noise.

Epoch Theta Rho Measurement Type

1899.385 173.0° 8.48" Pa – Photographic with

an astrograph

1988.130 178.7° 8.43" Eu – UCAC Catalog

1999.345 178.7° 8.43" E2 – 2MASS Survey

2000.341 178.8° 8.42" Ed – DENIS Survey

2017.244 179.2° 8.47" C – CCD/Two-dimensional

Electronic Imaging

Table 4. Current measurements and data available on WDS 12182-4251; measurements before 2017.244 are courtesy of the Washing-ton Double Star Catalog.



Conclusion Data from this study suggests that there has been a

small increase in both separation and position angle for DAM 1244 since its first recorded measurement in 1899. The four previous measurements from the WDS Catalog are generally consistent with the current astro-metric coordinates of the system. The proper motion measurements of the A and B components have been analyzed, and DAM 1244 may be considered a com-mon proper motion pair (CPM) until more accurate data is obtained. According to Harshaw’s classification sys-tem for CPMs, the rating of DAM 1244 also suggests that the pair may have an orbital solution. Therefore, while no conclusive claims can be made on the nature of this system as of now, there is a possibility that WDS 12182-4251 is gravitationally bound, despite there hav-ing been no drastic changes in motion.

Acknowledgments This study was made possible by the Boyce Re-

search Initiatives and Education Foundation (BRIEF) with Pat and Grady Boyce, and Cuesta College profes-sor Russell M. Genet offering their guidance and effort to the research team. Appreciation is extended to Srikar Namburi for recommendations during this project. The assertions made in this paper utilized information from the Washington Double Star Catalog, which is main-tained by the United States Naval Observatory, as well as the StelleDoppie and SIMBAD astronomical data-bases. The iTelescope network provided images of the system, and measurements were made using the Maxim DL, Mira64xPro, and SAODS9 software. Processing tools such as Microsoft Word and Excel were also em-ployed.

References

Genet, R., Johnson, J., Buchheim, R., and Harshaw, R. 2015, Small Telescope Astronomical Research Handbook. Ed. Collins, D.

Harshaw, R. 2014, Another Statistical Tool for Evaluat-ing Binary Stars. Journal for Double Star Observa-tions,10(1).

Mason, B. and Hartkopf, W. 2015, The Washington Double Star Catalog. Astrometry Department, U.S. Naval Observatory.

Mason, B. and Hartkopf, W. 2012, USNO CCD Astro-graph Catalog (UCAC). Astrometry Department, U. S. Naval Observatory.

Anushree Chaudhuri is a student from Westview High School in San Diego, California. She

is passionate about STEM subjects and the physical sciences. The Astronomy Research

Seminar presented an ideal opportunity to deepen her knowledge and experience in the

field of astronomy and astrophysics.

Figure 5. A scatterplot of previous measurements of DAM 1244.

ccd astrometric measurements and historical data summary ... · anushree chaudhuri is a student...

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